(a) Field of the Invention
The present invention relates to a skip-shift control method of an automatic transmission. More particularly, the present invention relates to a shift control method of an automatic transmission that controls a skip-shift from an N speed achieved by engagement of first and second frictional elements to an N−3 speed achieved by engagement of third and fourth frictional elements.
(b) Description of the Related Art
Generally, one frictional element is released and another frictional element is engaged according to a clutch-to-clutch shift control. However, during a specific skip-shifting process, two frictional elements may be released and two other frictional elements may be engaged.
Particularly, in the case of a kick-down 6 to 3 skip-shift where three speed steps are shifted, generally two frictional elements must be released and two other frictional elements must be engaged. However, it is understood that shift control of releasing two frictional elements and engaging two other frictional elements is hard to be realized.
Therefore, much research on two shifting processes that are successively performed in the case of a skip-shift, such as a 6 to 3 shift, has been conducted. For example, a 4 to 3 shift is performed after a 6 to 4 shift is completed so as to perform a 6 to 3 shift.
However, according to such a conventional 6 to 3 skip-shift control method, since two shifting processes are successively performed, shifting time may be taken long. That is, since the 4 to 3 shift is performed after the 6 to 4 shift is completed, the shifting time may be long.
In addition, since the 4 to 3 shift is performed after the 6 to 4 shift is completed, the shifting process may not be smoothly performed and a driver's shift feel deteriorates.
To solve such problems, many shift control methods of an automatic transmission where a first shift from a 6 speed to a 4 speed and a second shift from the 4 speed to a 3 speed are overlapped have been researched. In such a shift control method, a second shift from a middle speed between the 6 speed and the 3 speed to the 3 speed is overlapped with a first shift from the 6 speed to the middle speed when a 6 to 3 shift signal is detected.
However, according to such a shift control method, a shift torque of the middle speed may be generated and a double shift feel may be felt since shifting from the 6 speed to the 3 speed is performed by way of the middle speed. Further, shift shock may occur.
More concretely, in a case in which a shift is performed according to the conventional shift control method, a turbine speed remains at the middle speed for a while, and output torque fluctuates seriously, as shown in FIG. 6.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.